Method and installation for gasifying carbonaceous compounds

ABSTRACT

The invention relates to a method of gasifying carbon-containing compounds incorporating mineral elements and/or potential contaminants, and it also relates to a gasification installation having means for containing a bath of molten slag, means for charging said compounds into said bath, means for injecting at least oxidizer into the bath so that the mixture of carbon-containing compounds and oxidizer is super-stoichiometric, whereby a first fraction of the compounds is pyrolyzed, a second fraction is subjected to a combustion reaction suitable for delivering heat energy to the bath of slag, and a third fraction diffuses into the bath, means for recovering the gas given off by the pyrolysis and the combustion of the first and second fractions, and means for lowering the temperature of a portion of the molten slag so as to allow it to solidify, thereby immobilizing at least a portion of the third fraction of the compounds containing mineral elements and/or potential contaminants.

[0001] The present invention relates to a method of gasifying compoundsof the type containing carbon, and more particularly compounds that alsocontain mineral elements and/or potential contaminants. The presentinvention also relates to an installation for implementing the method.

[0002] An intended field of application lies particularly in recyclingorganochemical, or petrochemical, and treated-wood residues.

[0003] Methods of gasifying carbon-containing compounds are well knownand lead to various gases being produced as a function of the initialingredients and the temperature conditions in which the chemicalreactions take place. These reactions include the following inparticular:

C+O₂=CO₂

C+½O₂=CO

C+CO₂=2CO

C+H₂O=CO+H₂

CO+H₂O CO₂+H₂

[0004] The reactions take place more or less completely and as a generalrule they produce a mixture of gases comprising in particular bothcarbon dioxide and hydrogen.

[0005] The Winkler method is well adapted to gasifying coal and itoperates with a fluidized bed, enabling a mixture of carbon monoxide andof hydrogen to be produced. However that method is poorly adapted to theintended types of fuel, in particular because particles of wood areeasily blown away. Mention can also be made of the Lurgi method, whichis fed with granular coal and operates in a fixed bed under pressure,but at low temperature, thereby causing numerous harmful compounds to begiven off which must then be recovered by filtering the flue gases in anoil washing column.

[0006] Furthermore, in those methods which are specifically designed toproduce gas from coal, no provision is made to render inert anycontamination or to remove any mineral elements that might be containedin the coal. Unfortunately, the types of fuel envisaged contain mineralelements and above all contaminants, in particular chromium and copperwhich must be recovered and made inert.

[0007] An object of the present invention is to provide a method ofgasifying a compound containing mineral elements and/or potentialcontaminants, in which the mineral elements are removed, together withthe contaminants which are made inert.

[0008] To achieve this object, the invention provides a method ofgasifying compounds, in particular carbon-containing compoundsincorporating mineral elements and/or potential contaminants, the methodbeing characterized in that it comprises the following steps:

[0009] charging at least said compounds into a bath of molten slag andinjecting oxidizer into said bath so that the mixture ofcarbon-containing compounds and oxidizer is super-stoichiometric,whereby a first fraction of said compounds is pyrolyzed, a secondfraction is subjected to a combustion reaction suitable for deliveringheat energy to said bath of slag, and a third fraction diffuses intosaid bath;

[0010] recovering the gases that result from the pyrolysis and thecombustion of said first and second fractions; and

[0011] cooling at least a portion of the molten slag so as to solidifyit, thereby immobilizing at least a portion of said third fraction ofsaid compounds containing at least the mineral elements and/or thepotential contaminants.

[0012] Thus, a characteristic of the gasifying method lies in the mediumconstituted by the molten slag, within which the carbon-containingcompounds that might also contain mineral elements and/or potentialcontaminants are decomposed by pyrolysis. Under the action of atemperature lying in the range 1100° C. to 1500° C. , thecarbon-containing compounds form new chemical species producing asynthetic gas while the non-volatile potential contaminants diffuse intothe molten slag.

[0013] The injected oxidizer and the newly formed chemical speciesconstitute a mixture which, under the effect of temperature, leads to acombustion reaction.

[0014] It will be understood that combustion is always exothermal andtherefore provides the heat energy needed by the slag to enable it tomaintain a high temperature.

[0015] Nevertheless, an object of the invention is to produce syntheticgas, and in order to do so the proportions of the carbon-containingcompounds, i.e. fuel, and of oxidizer are adjusted so that the mixtureis super-stoichiometric. Thus, the quantity of fuel is greater than thequantity of oxidizer available for reacting with it and therefore afirst fraction of the carbon-containing compounds is pyrolyzed toprovide synthetic gas while a second fraction is burned to deliverenergy to the slag.

[0016] Both the burned gas and the gas derived from pyrolysis arerecovered, but it will be understood that it is only thepyrolysis-derived gas that is of interest, whether as a source of energyor for performing various kinds of synthesis.

[0017] In addition, in order to immobilize the contaminants contained inthe molten slag, its temperature is lowered by casting it, andsubsequently it is granulated. When the method is performedcontinuously, it is advantageous to lower the temperature of a portionof the molten slag by removing said portion. This operation consists incasting slag either sequentially or continuously.

[0018] In order to make the slag inert, and in particular to make up forthe removed slag so as to maintain a constant level for the bath, it isadvantageous to add flux to the molten slag.

[0019] To implement the method, and when so required by the form of thecompounds, it is advantageous to prepare said compounds in the form ofsolid elements so as to enable said elements to be charged verticallyover the bath of molten slag, thus enabling said elements to bedeposited on the surface of said bath and/or to incorporated therein.

[0020] When heterogeneous and volatile materials are introduced abovethe molten slag, and given the gases that are being given off, thematerials run the danger of not reaching the slag directly, and of beingcarried away with the gases. To mitigate that problem, said compoundsare agglomeratized to make solid lumps that are heavy relative to thegases being given off, so as to ensure that said compounds areintroduced directly into the slag bath.

[0021] When the carbon-containing compounds are sufficiently homogenousand dry, it is preferable for said compounds to be injectedsimultaneously with the oxidizer into the bath of molten slag.

[0022] In advantageous manner, both during starting stages and wheneverthe quantity of energy delivered to the slag by the combustion of thecarbon-containing compounds is too low, it is also possible to injectsaid oxidizer into said bath of molten slag simultaneously with a fuelso as to produce a combustion reaction to deliver heat energy to saidbath and keep it at the desired temperature.

[0023] Nevertheless, the object of the present invention is to recoverthe energy contained in the carbon-containing compounds, and inparticular to recover gases, and in accordance with a particularcharacteristic of the invention said gases are purified so as to obtaina clean fuel gas. The gas can be burned on site in a power station or itcan be delivered to a distribution network with or withoutco-generation.

[0024] The gas coming directly from the combustion reaction and thepyrolysis is hot, and in accordance with another particularcharacteristic, the heat energy, in particular from said gas, isrecovered so as to deliver the heat energy to a heat-conveying fluid. Inaddition, a fourth fraction of said compound vaporized by the bath ofmolten slag is condensed. Some of the elements contained in thecarbon-containing compounds do not participate in the pyrolysis orcombustion reactions and they vaporize on coming into contact with theslag. These elements are isolated in the heat exchanger since it is theheat exchanger which contributes to condensing said fourth fraction.

[0025] The present invention also provides an installation for gasifyingcompounds, in particular carbon-containing compounds having a mineralelement and/or potential contaminants, said installation comprising:

[0026] means for containing a bath of molten slag;

[0027] means for charging at least said compounds into said bath ofmolten slag;

[0028] means for injecting at least oxidizer into said bath so that themixture of carbon-containing compounds and oxidizer issuper-stoichiometric whereby a first fraction of said compounds ispyrolyzed, a second fraction is subjected to a combustion reactionsuitable for delivering heat energy to said bath of slag, and a thirdfraction diffuses into said bath;

[0029] means for recovering in particular the gases that result from thepyrolysis and the combustion of said first and second fractions; and

[0030] means for lowering the temperature of at least a portion of themolten slag so as to cause it to solidify, thereby immobilizing at leasta portion of said third fraction of said compounds containing at leastmineral elements and/or potential contaminants.

[0031] In a preferred embodiment of the invention, the bath of moltenslag is contained in the bottom portion of a vertical cylindricalfurnace having at least one opening pierced through the wall of the topportion of said furnace for charging it with said compounds, and atleast one opening pierced through the wall of the bottom portion of saidfurnace for extracting at least a portion of the molten slag.

[0032] It will be understood that the carbon-containing compounds aredropped into the molten slag from the top of the furnace in order to betransformed, and that the same applies to adjusting the slag when aportion is extracted. When the carbon-containing compounds reach themolten slag, they are transformed into gas, and in accordance with thecharacteristic of the invention, the wall of the top portion of thevertical furnace is pierced by an orifice for collecting at least thegas produced by pyrolysis and by combustion of said first and secondportions, and said installation further comprises washing meansconnected to said orifice to purify said gas.

[0033] On leaving the furnace, the gas possesses a large amount ofenergy since it reaches a temperature that is well above 1100° C. Inorder to improve the overall efficiency of the installation, a heatexchanger and deposition chambers are interposed between the furnace andthe washing means so as to recover at least a portion of the heat energyof said product and so as to recover in condensed form a fourth fractionof the compounds vaporized in the furnace.

[0034] The gas escapes via the orifice pierced thorough the top portionand passes through the set of devices so as to obtain clean gas. Inorder to prevent the gas escaping via the opening that is provided forcharging purposes, it is advantageous for the means for charging saidcompounds to comprise a feed screw opening out above the bath of moltenslag and provided with heater means so as to agglomerate the compoundsby causing at least one of said compounds to melt. It will be understoodthat the feed screw located at the opening for charging the furnaceenables the enclosure constituted by the furnace to be isolated while itis in operation and contains carbon-containing compounds. The fact thatsome of the compounds become semisolid and cause other compounds tobecome agglomerated contributes to ensuring that the feed openingremains impermeable to the bulk of the gas.

[0035] This gas results essentially from decomposition of thecarbon-containing substances as induced indirectly by the heat given offby burning a fraction of said substances, which combustion requires anoxidizer.

[0036] In a particular embodiment, the means for injecting oxidizer intothe molten slag comprise a blast pipe passing through the wall in thetop portion of the furnace and dipping into the bath of molten slag, andwithin which the oxidizer is under pressure.

[0037] In another particular embodiment, the means for injectingoxidizer into the molten slag comprise a blast pipe passing through thewall constituting the bottom portion of the furnace and opening out intothe bath of molten slag, the blast pipe containing oxidizer underpressure.

[0038] In both of these embodiments, the end of the blast pipe isimmersed in the slag, and the oxidizer under pressure diffuses throughthe slag in order to react with the fuel.

[0039] In the second particular embodiment, the opening pierced throughthe bottom portion of the wall of said furnace advantageously opens outin a tank adjacent to said furnace and having an open top, the sides ofthe tank being at least as high as the mean level of the bath of moltenslag contained in the bottom portion of said furnace, and said blastpipe is inserted into said open top portion and passes through the wallcommon to the bottom portion of the furnace and said tank so as topenetrate into the bath of molten slag. These dispositions serve inparticular to overcome the difficulties of sealing the place where theblast pipe passes through the wall of said furnace.

[0040] In addition, said tank makes it easier to cast slag, inparticular in a continuous process, since it suffices to provide a notchin the sides of the tank level with the bath of molten slag. Thus, eachtime slag is adjusted, its depth increases and consequently a fractionof the molten slag runs off.

[0041] Other features and advantages of the invention appear on readingthe following description given by way of non-limiting indication andwith reference to the accompanying drawings, in which:

[0042]FIG. 1 is an overall diagrammatic view of a gasificationinstallation for implementing the method of the invention;

[0043]FIG. 2 is a simplified vertical section view of the furnace in aparticular embodiment of the installation;

[0044]FIG. 3 is a diagrammatic section view on plane III-III of FIG. 2;and

[0045]FIG. 4 is a diagrammatic section view on plane IV-IV of FIG. 2.

[0046] With reference initially to FIG. 1, there follows a generaldescription of an installation for implementing the gasification methodof the invention.

[0047] The reactor 2 is referred to as a furnace and constitutes theessential element of the installation since it is within the reactorthat all of the transformations of the invention take place.

[0048] The furnace 2 is made of refractory material in the form of avertical cylinder of height greater than its diameter. The diameter ofsuch a furnace is fixed as a function of the quantities ofcarbon-containing compounds that are to be transformed, and itpreferably lies in the range 2 meters (m) to 4 m, making it possible tooptimize overall efficiency.

[0049] Slag 4 is placed in the bottom portion of the furnace 2 andduring an initial stage it is heated by means of a blast pipe 6 with afuel and an oxidizer burning at the end of the pipe, said fuel andoxidizer being injected under pressure. The end of the blast pipe isthrust into the slag causing it to melt, and as a result the molten slagconstitutes a bath whose temperature can lie in the range 1100° C. to1500° C.

[0050] In this embodiment, the blast pipe passes through the wallconstituting the top portion 8 of the furnace 2 and the pipe is movablealong the axis of the furnace so that its flame can be immersed in theslag. Fuels suitable for this purpose are preferably gas or fuel oil,and the oxidizer is generally pure air or oxygen-enriched air.

[0051] In a second stage, i.e. during normal operation, heat energy isdelivered to the slag 4 by controlled combustion of thecarbon-containing compounds 10 floating on the bath of the slag. Thesecompounds are charged from a hopper 12 onto the bath of slag 4 by meansof a feed screw 14.

[0052] The carbon-containing compounds that are suitable for beingtransformed in the furnace 2 are essentially wood and hydrocarbons. Thewood used to make posts for supporting low voltage electricity lines ortelephone lines is generally treated with hydrosoluble salts, forexample solutions of oxides of copper, chromium, and arsenic, and thewood used for railway sleepers or ties is treated with creosote. Suchwood and any other wood treated with the same substances is difficult torecycle, and the gasification method of the invention enables theharmful contaminants contained therein to be destroyed or to berecovered and made inert.

[0053] The wood is prepared in the form of fragments and the finefraction thereof is agglomerated using carbochemical or petrochemicalresidues. Bituminous shale can also be used in this gasification method.

[0054] The wood in the form of shavings and sawdust is placed in thehopper 12 together with carbochemical or petrochemical residues so as toform a mixture, said hopper 12 being extended by a feed screw 14 leadingto an opening 16 through the wall constituting the top portion 8 of thefurnace 2. The feed screw 14 is hermetically connected to the furnace 2and it is provided with a heater system which surrounds it so that assaid mixture passes along the feed screw, the residue softens andtogether with the shavings and sawdust makes uniform pieces that can betreated as solid lumps.

[0055] When these solid lumps come over the opening 16 they drop intothe furnace 2 and are deposited onto the surface of the bath of moltenslag 4.

[0056] When the carbon-containing compounds are initially in the form oflumps or pellets, or when a feed screw is not suitable for charging thefuel, an airlock or any other device for performing the same function isprovided so as to enable said compounds to be introduced to the slag 4,while preventing gas from leaking out of the furnace 2.

[0057] These lumps made up essentially of carbon-containing compounds 10decompose under the effect of the heat so as to form new substances, andin particular gases. Some of these compounds, constituting said fourthfraction are vaporized, and this applies in particular to the water andthe arsenic. The arsenic is in oxidized form in the burden, but theconditions within the furnace reduce it to the metal state; it thereforecondenses in its metal form, thus improving elimination thereof.

[0058] The blast pipe 6 which was used during the initial stage forinjecting both fuel and oxidizer into the slag 4 so as to delivercombustion energy to said slag, is used during this second stage todeliver the oxidizer needed for controlled combustion of thecarbon-containing compounds 10 present on the surface of the bath ofmolten slag 4. Thus, the controlled combustion of the carbon-containingcompounds suffices on its own to deliver the heat energy required forkeeping the temperature of the bath in the range 1100° C. to 1500° C.

[0059] As during the first stage, the oxidizer is injected from the endof the blast pipe into the core of the slag. As a result, said oxidizerdiffuses through said slag 4 and reacts with the carbon-containingcompounds 10 in a combustion reaction. The oxidizer is constituted bypure air, by oxygen, or by a mixture thereof, and it is adjusted as afunction of the oxidizing properties that are required. The oxidizerflow rate is also adjusted so that the mixture of carbon-containingcompounds 10 and oxidizer is super-stoichiometric, thus ensuring thatonly said second fraction of the carbon-containing compound is burnt todeliver the energy required for keeping the slag melted. The remainderof the carbon-containing compounds, said first fraction, is thuspyrolyzed and forms new substances, and in particular carbon monoxideand hydrogen.

[0060] The carbon-containing compounds are likely to contain potentialcontaminants which spread through the molten slag during decomposition.This applies in particular to chromium and to copper. Chromium formsslag while cooper dissolves in the slag if its concentration is verylow, otherwise it serves as a basis for forming a dense phase in metalor other form. In order to immobilize these elements, slag is drawn offat regular intervals or continuously and is then granulated. This takesplace through an opening (not shown in FIG. 1) pierced through the wallconstituting the bottom portion of the furnace 2. To compensate for slagbeing extracted, the slag is made up by using conventional fluxes of thelimestone, sand, iron ore, sodium carbonate, etc. type. Addition cantake place through the opening formed in the wall forming the topportion 8 and used for charging the carbon-containing compounds. Howeverit is preferable to provide a special opening (not shown) for chargingflux, said opening being pierced through the wall forming the topportion 8.

[0061] The appearance of gas above the slag produces gas pressure withinthe furnace, and said gas tends to escape via an orifice 18 formedthrough the wall constituting the top portion 8 of the furnace 2. Anupdraft of gas thus appears in the furnace and it is necessary for thelumps of carbon-containing compounds to be dense enough to be able tofall through the updraft and reach the molten slag 4 without beingentrained by the gas.

[0062] The temperature of the gas is generally higher than 1100° C., andconsequently in order to optimize the energy efficiency of theinstallation, at least part of the heat energy of said gas is recoveredby passing the gas through a chamber 20 that includes a heat exchanger22. The heat exchanger is constituted by a coil carrying aheat-conveying fluid suitable for actuating a turbine, for example.

[0063] The gas cools down on contacting the heat exchanger 22 andcertain compounds, constituting said fourth fraction, condense, and inparticular arsenic condenses at about 800° C. A space 24 is provided inthe chamber 20 for storing the arsenic condensation dust. A secondanalogous chamber (not shown) can also be provided upstream from thefirst for allowing the dust that comes directly from the furnace 2 tosettle. This dust can be recycled and reinserted as part of preparingthe charge.

[0064] Once the gas temperature has dropped to about 200° C., theefficiency of the heat exchanger 22becomes relatively poor and the gasis removed. It is passed through washing means 26 connected to thechamber 20 to eliminate the last traces of dust and also the unwantedgases so as to deliver a clean gas at an outlet 28. A main fan (notshown) is provided to drive the gas from the outlet 28 and direct it toa gas holder. The main fan is suitable for establishing suction at theend of the gasification installation, thus contributing to recoveringthe gases that come from the furnace.

[0065] The washing water is recycled through a purifier 30 and is thenreused. Provision is also made to interpose a flare 32 so as to be ableto burn off the gas in the event of an incident, and most particularlyduring start-up and closing-down stages.

[0066] A clean synthetic gas is thus obtained that is suitable for useas a fuel, but that could alternatively be used as raw material forproducing various organic compounds.

[0067] Reference is now made to FIGS. 2, 3,and 4in order to describe thebottom portion of the furnace in greater detail for a particularembodiment.

[0068]FIG. 2 is a vertical section view through the furnace 2 in whichthe wall forming the bottom portion of the furnace is pierced by anopening 34 leading to a tank 36, or fore-hearth in connection with thebottom portion of the furnace 2. The top of the fore-hearth 36 is openand its sides 38 are somewhat taller than the mean level of the bath ofmolten slag 4 in the furnace 2. It will be understood that the moltenslag 4 reaches the fore-hearth 36 and that the level of the slag matchesthe level of the slag 4 in the furnace 2.

[0069] In this particular embodiment, the blast pipe 6 is insertedthrough the open top portion of the fore-hearth 36 and passes obliquelythrough the wall that is common to the bottom portion of the furnace 2and to the fore-hearth 36 so that its end 40 opens out into the bath ofmolten slag in the furnace. The oxidizer is thus injected into the slag4 in the furnace and diffuses up to its surface so as to enable thecarbon-containing compounds to burn. This embodiment serves inparticular to avoid problems associated with the joint between the blastpipe 6 and the furnace 2 when the blast pipe passes through the topportion of the furnace.

[0070]FIG. 4 shows the blast pipe 6, the furnace 2, and the fore-hearth36 in a plan view on section plane IV-IV. The blast pipe 6 is to oneside of the center of the furnace 2, so injecting oxidizer causes themolten mass to swirl, thus improving stirring and providing goodcirculation of slag 4 through the fore-hearth so as to ensure that theslag does not solidify therein. For this purpose, the orifice 42 in thewall through which the blast pipe passes is at least as large as theopening 34 pierced in the wall constituting the bottom portion of thefurnace. Furthermore, as can be seen in FIG. 3, the opening 34 is alsooff-center and extends tangentially to the inside wall of the furnace soas to lead to a corner of the fore-hearth.

[0071] This configuration reduces the length of time molten slag 4spends transiting through the fore-hearth and consequently reduces therisk of the slag solidifying therein. To further reduce this risk, thefore-hearth is advantageously provided with a lid (not shown) thatpresents an orifice through which the blast pipe passes.

[0072] The slag is drawn off at regular intervals or continuouslythrough a channel 44 formed in the wall of the fore-hearth, and capableof being opened and closed under control. The slag is then granulatedand can be used as aggregate or as a sand-blasting agent since thepotential contaminants it contains are completely immobilized.

[0073] In addition, a drawing-off hole is provided at the bottom of thefore-hearth, which hole is normally plugged, and serves to eliminate adense phase that forms and becomes deposited at the bottom of the bathof molten slag.

[0074] The invention is illustrated below by way of a comparativeexample in which three different compositions of oxidizer were injectedinto the molten slag. The example gives values for the amounts of energythat an installation of the invention can be expected to produce byvarying the composition of the oxidizer.

[0075] The values and the -compositions given below relate to a mixturecomprising 70.6% wood and 29.4% pitch. The wood contained 15% moistureand 0.8% ash, and the “pitch” contained 80% pure pitch and 20% earth. Toenable the earth to melt easily, appropriate corrections were made tothe slag, e.g. by supplying iron oxide.

[0076] The data given below applies to consuming 4722 kilograms per hour(kg/h) of wood and pitch mixture, and drawing off 9 (metric) tonnes ofslag per day using a furnace having a diameter of 2 m. Naturally, theslag was readjusted as a function of the quantity drawn off. Oxidizer %oxygen 21 30 40 in air stp gas production 14,499 11,099 9,468 rate(m³/h) H₂ % 14.3 21.2 26.3 CO % 21.6 30.4 36.9 CO₂ % 8.4 8.7 8.9 N₂ %55.8 39.7 27.9 Combustion 1399° C. 1654° C. 1794° C. temperature NCV inkcal/m³ at 980 1405 1719 stp “Real” NCV Mcal/h 14,209 15,594 16,275Steam kg/h 7116 5499 4719

[0077] The greater the oxygen content of the oxidizer the smaller thequantity of gas that is produced. However, conversely, the gas thatresults from the transformation is richer in carbon monoxide and inhydrogen, thus giving it a greater net calorific value (NCV).

[0078] Nevertheless, the quantity of steam produced decreases withincreasing oxygen, and above all oxygen is expensive and that needs tobe taken into consideration in determining the overall efficiency of theinstallation.

[0079] In the above example, the method can be optimized easily bymodulating the flow rate of oxygen and air. For some other compositionof carbon-containing compounds, new adjustments of the oxidizer arenecessary.

1/ A method of gasifying compounds, in particular carbon-containingcompounds incorporating mineral elements and/or potential contaminants,the method being characterized in that it comprises the following steps:charging at least said compounds into a bath of molten slag andinjecting oxidizer into said bath so that the mixture ofcarbon-containing compounds and oxidizer is super-stoichiometric,whereby a first fraction of said compounds is pyrolyzed, a secondfraction is subjected to a combustion reaction suitable for deliveringheat energy to said bath of slag, and a third fraction diffuses intosaid bath; recovering the gases that result from the pyrolysis and thecombustion of said first and second fractions; and cooling at least aportion of the molten slag so as to solidify it, thereby immobilizing atleast a portion of said third fraction of said compounds containing atleast the mineral element and/or the potential contaminants. 2/ Agasification method according to claim 1, further characterized bypreparing said compounds in the form of solid lumps so as to enable saidlumps to be charged vertically over the bath of molten slag, wherebysaid lumps are deposited on the surface of said bath. 3/ A gasificationmethod according to claim 1 or claim 2, further characterized bysimultaneously injecting said compounds and the oxidizer into the bathof molten slag. 4/ A gasification method according to any one of claims1 to 3, characterized by simultaneously injecting said oxidizer and afuel into said bath of molten slag to produce a combustion reactionwhereby heat energy is delivered to said bath. 5/ A gasification methodaccording to any one of claims 1 to 4, further characterized bycondensing out a fourth fraction of said compounds as vaporized by thebath of molten slag. 6/ A gasification method according to any one ofclaims 1 to 5, further characterized by purifying said gases so as toobtain a clean fuel gas. 7/ A gasification method according to any oneof claims 1 to 6, further characterized by recovering heat energy, inparticular from said gas, so as to deliver heat energy to aheat-conveying fluid. 8/ A gasification method according to any one ofclaims 1 to 7, further characterized by adding fluxes in particular tothe molten slag. 9/ A gasification method according to any one of claims1 to 8, characterized in that the temperature of a portion of the moltenslag is lowered by extracting said portion. 10/ An installation forgasifying compounds, in particular carbon-containing compoundsincorporating mineral elements and/or potential contaminants, theinstallation being characterized in that comprises: means for containinga bath of molten slag; means for charging at least said compounds intosaid bath of molten slag; means for injecting at least oxidizer intosaid bath so that the mixture of carbon-containing compounds andoxidizer is super-stoichiometric whereby a first fraction of saidcompounds is pyrolyzed, a second fraction is subjected to a combustionreaction suitable for delivering heat energy to said bath of slag, and athird fraction diffuses into said bath; means for recovering inparticular the gases that result from the pyrolysis and the combustionof said first and second fractions; and means for lowering thetemperature of at least a portion of the molten slag so as to cause itto solidify, thereby immobilizing at least a portion of said thirdfraction of said compounds containing at least mineral elements and/orpotential contaminants. 11/ A gasification installation according toclaim 10, characterized in that the bath of molten slag is contained inthe bottom portion of a vertical cylindrical furnace having at least oneopening pierced through the wall of the top portion of said furnace forcharging it with said compounds, and at least one opening piercedthrough the wall of the bottom portion of said furnace for extracting atleast a portion of the molten slag. 12/ A gasification installationaccording to claim 10 or claim 11, characterized in that the means forcharging said compounds comprise a feed screw opening out verticallyabove the bath of molten slag and provided with heater means whereby thecompounds can agglomerate together by at least one of said compoundsmelting. 13/ A gasification installation according to any one of claims10 to 12, characterized in that the means for injecting oxidizer intothe molten slag comprise a blast pipe passing through the wall of thebottom portion of the furnace to open out into the bath of molten slag,and in which the oxidizer is under pressure. 14/ A gasificationinstallation according to claim 13, characterized in that the openingpierced through the wall of the bottom portion of said furnace leads toa tank adjacent to said furnace, having an open top and sides that comeup at least to the mean level of the bath of molten slag contained inthe bottom portion of said furnace, and in that said blast pipe isinserted into said open top portion and passes through the wall commonto the bottom portion of the furnace and said tank so as to open outinto the bath of molten slag. 15/ A gasification installation accordingto any one of claims 10 to 12, characterized in that the means forinjecting oxidizer into the molten slag comprise a blast pipe passingthrough the wall of the top portion of the furnace and penetrating intothe bath of molten slag, and in which the oxidizer is under pressure.16/ A gasification installation according to any one of claims 11 to 15,characterized in that the wall of the top portion of the verticalfurnace is pierced by an orifice for collecting at least the gasesderived from the pyrolysis and the combustion of said first and secondfractions, and in that said installation further comprises washing meansconnected to said orifice in order to purify said gas. 17/ Agasification installation according to claim 16, characterized in that aheat exchanger and deposition chambers are interposed between thefurnace and the washing means so as to recover at least part of the heatenergy from said products and so as to recover in condensed form afourth fraction of the compounds which are vaporized within the furnace.